You’d be correct in assuming that next-server is set as per default by the FOG installation script.

If i understand you correctly, your suggestion of trunking would enable the client to connect to the TFTP server on either link? I’d rather not, as the other link is only 100Mbps on some cheap Cisco 2960 SI series.

Ideally the clients would choose the correct link matching the network ID of the next-server.